The present invention relates to motor starters, and particularly, motor starters for industrial applications which employ electromechanical contactors or static solid state devices for connecting and disconnecting electrical power to large motors.
There are two basic types of motor starters -- electromechanical and static. The electromechanical motor starters employ contactors such as that disclosed in U.S. Pat. No. 4,006,440 issued on Feb. 1, 1977, in circuits such as those disclosed in U.S. Pat. Nos. 3,121,826 issued on Feb. 18, 1964 and 3,575,637 issued on Apr. 20, 1971. In contrast, solid state, static motor drives employ SCRs and triacs to control the power delivered to the motor and they are characterized by elaborate control circuits such as that disclosed in U.S. Pat. No. 3,614,596 issued on Oct. 19, 1971. Both types of motor starters have desirable characteristics and features which are unique to each.